1. Field of the Invention
This invention relates to time base servo tape storage devices and more particularly relates to the use of velocity proportional clocking to correct tape drive track following problems with regard to head position.
2. Description of the Related Art
Modern technological trends have led to the heavy reliance of businesses on electrical and magnetic data storage devices. In particular, magnetic tape storage devices have become popular for their low cost and high data capacities. As a result, demand has also increased for tape storage devices with improved reliability, speed, and bit density. With regard to linear tape devices, there have been significant increases in recording density (meaning there is more information stored on a given length of tape) as well as track density (meaning there are more data tracks stored across the width of the tape). The continued increase in density, however, has led to the need for more accurate servo control systems that allow for more precise track following.
In order to implement more precise track following, many entities are now using time base servos that utilize a measurement of the time between servo stripe signal peaks to correct the head position. One side effect of this is that noise caused by tape signal dropout due to media defects may corrupt the signal resulting in a misplaced head position. Some of these defects have been overcome by implementing a combination of Hipass, Lowpass, and Bandpass filters which are usually realized digitally as IIR (Infinite Impulse Response) or FIR (Finite Impulse Response) filters. Because tape drives are usually required to operate at many different velocities, different filter coefficients must be designed for each desired velocity. This can result in high design and implementation costs.
In one embodiment, an Analog-to-Digital Converter (ADC) is used to sample the signal stored on the magnetic tape. Current technology uses the same sampling rate regardless of the tape velocity, meaning there are a different number of samples per cycle for each different velocity. This can result in high costs because separate difference equalizer settings must be designed for each of the different operating velocities. By using velocity proportional clocking, one equalizer setting can be used for all velocities.
Another problem with current time base servo designs relates to the peak time measurement methods used to produce the corrective feedback signal. In one embodiment, a high frequency clock is used to count the time, or clock cycles, that occur between uniform signal peaks formatted on the magnetic tape. As the tape velocity fluctuates from one operating velocity to another, the count can become very large at slower velocities (resulting in overflow) or very small at higher velocities (resulting in a lack of resolution). Errors caused by overflow or a lack of resolution can lead to inaccurate head positions and costly inefficiencies. By varying the clock frequency proportional to the tape velocity, the steady state counter value can be fixed using a reference value, thereby reducing the possibility of counter errors.
From the foregoing discussion, it should be apparent that a need exists for an apparatus, system, and method for the velocity proportional clocking of time base servo tape storage devices. Beneficially, such an apparatus, system, and method would reduce production costs by eliminating resolution and overflow problems, eliminating the need for multiple filter designs corresponding to each operating velocity, and eliminating the need for multiple difference equalizer designs.